Exposed bus bar

[John Controls]

I am considering a design change for one of our machines. For some time we have used a Safety Switch on the hinged door of an enclosure that I would classify as a junction box. The box is 16 X 20 and contains exposed bus-bars (3 X 480V) that interconnect multiple heating elements behind the enclosure. The Safety Switch will disengage a contactor in the main control enclosure that removes power to the bus-bars, when the enclosure door is open. I disagree with the entire concept and propose the elimination of the switch entirely as I do not see where it complies with any code and in fact creates a false sense of safety. The problem I am having is that when the door is open the bus-bars are exposed, unlike the connections in a motor doghouse which are insulated. Any thoughts or knowledge on code that discusses exposed bus-bars in a junction box?

 

[GoldDigger]

I am considering a design change for one of our machines. For some time we have used a Safety Switch on the hinged door of an enclosure that I would classify as a junction box. The box is 16 X 20 and contains exposed bus-bars (3 X 480V) that interconnect multiple heating elements behind the enclosure. The Safety Switch will disengage a contactor in the main control enclosure that removes power to the bus-bars, when the enclosure door is open. I disagree with the entire concept and propose the elimination of the switch entirely as I do not see where it complies with any code and in fact creates a false sense of safety. The problem I am having is that when the door is open the bus-bars are exposed, unlike the connections in a motor doghouse which are insulated. Any thoughts or knowledge on code that discusses exposed bus-bars in a junction box?

There is no intrinsic danger from 480V bus bars if no power is applied to them.
The only part of your argument that I agree with is that it is not safe to assume that the bus bars are not powered just because the safety switch is present. Proper LOTO and voltage verification is also needed.

If you remove the safety switch, then at a minimum you would want to put a lock on the enclosure, even if you insulate the bus bars.

To me your proposal is like saying that all trapeze artists must work without a net since the net gives a false sense of security.

 

[John Controls]

But, have you ever saw a motor doghouse cover with a safety switch? If it had a switch would you be inclined to replace the motor by trusting the switch? Is the switch needed if LOTO procedures are followed? Have you ever saw a motor dog house cover with a lock? I appreciate your reply but am hoping to find something (a standard or code) that would clarify this for me.

 

[donaldelectrician]

I am considering a design change for one of our machines. For some time we have used a Safety Switch on the hinged door of an enclosure that I would classify as a junction box. The box is 16 X 20 and contains exposed bus-bars (3 X 480V) that interconnect multiple heating elements behind the enclosure. The Safety Switch will disengage a contactor in the main control enclosure that removes power to the bus-bars, when the enclosure door is open. I disagree with the entire concept and propose the elimination of the switch entirely as I do not see where it complies with any code and in fact creates a false sense of safety. The problem I am having is that when the door is open the bus-bars are exposed, unlike the connections in a motor doghouse which are insulated. Any thoughts or knowledge on code that discusses exposed bus-bars in a junction box?

Quite Frankly i do not know of any code that deals with exposed bus bars in equipment or Heaters, ect .

If there is a Disco , I would think it will disco that peice of equipment , like a Bus Bar Switch / Disco for the feed dropped

is that what you are asking ...

There rules for spacing and clearances , i believe .


Exposed bus bars are not inherently dangerous or uncommon .

Qualified persons are to service this equipment .... That is the catch ,,, Should be behind locked doors / cabinet .


Hope that helps


Don

 

[zbang]

I expect that any requirements would come out of OSHA or UL/FM. After that, why not just put a piece of Plexiglas with a warning sign over the bus bars. About all the sign would need to say is something like "Danger: Energized parts 480VAC" and "Qualified personnel only"; I'm sure you can buy stock stickers with the right icons and words.

 

[don_resqcapt19]

Most electrical equipment has exposed live parts when you open the cover.
The closest the NEC comes to addressing this question is the power distribution block rule in 314.28(E). This rule is fairly new to the code.

I really don't have a problem with the exposed live parts when the door is open, I do, however, have a problem with a disconnect that does not directly disconnect the power as appears to be the case here.

 

[petersonra]

I am considering a design change for one of our machines. For some time we have used a Safety Switch on the hinged door of an enclosure that I would classify as a junction box. The box is 16 X 20 and contains exposed bus-bars (3 X 480V) that interconnect multiple heating elements behind the enclosure. The Safety Switch will disengage a contactor in the main control enclosure that removes power to the bus-bars, when the enclosure door is open. I disagree with the entire concept and propose the elimination of the switch entirely as I do not see where it complies with any code and in fact creates a false sense of safety. The problem I am having is that when the door is open the bus-bars are exposed, unlike the connections in a motor doghouse which are insulated. Any thoughts or knowledge on code that discusses exposed bus-bars in a junction box?

no one is supposed to be working in such a way as to be exposed to energized parts anyway.

IMO, using a contactor in any way as part of a "safety" circuit means that it is not a safety circuit anymore. It certainly cannot be part of a LOTO system.

 

[wbdvt]

Another consideration with exposed bus bar is arc flash. Until the bus bars are tested to be de-energized the proper Arc Rated PPE needs to be worn when opening the door and testing the bus bars. After the bus bars have been proven to be de-energized, then the Arc Rated PPE is no longer needed.